Seat back



FIG. 1 is a left front perspective view of a first embodiment of a seat back showing my new design and including broken lines indicating representative environmental elements;

FIG. 2 is an enlarged front elevational view thereof;

FIG. 3 is an enlarged side elevational view, the opposite side being a mirror image thereof;

FIG. 4 is an enlarged rear elevational view thereof;

FIG. 5 is a left front perspective view of a second embodiment of a seat back showing my new design with the front portion of the seat back covered and including broken lines indicating representative environmental elements;

FIG. 6 is an enlarged front elevational view thereof;

FIG. 7 is an enlarged side elevational view, the opposite side being a mirror image thereof; and,

FIG. 8 is an enlarged rear elevational view thereof.

The views of the seat back not shown form no part of the claimed design. The broken lines depicting a seat and legs in FIGS. 1 and 8 represent environmental elements only and form no part of the claimed design. 

The ornamental design for a seat back, as shown and described. 